Heparanase Plays a Dual Role in Driving Hepatocyte Growth Factor (HGF) Signaling by Enhancing HGF Expression and Activity

Hepatocyte growth factor (HGF) is a heparin-binding cytokine that enhances growth, motility, and angiogenesis of many tumor types, including multiple myeloma where it is often highly expressed. However, little is known regarding what controls HGF level and activity in these tumors. Evaluation of bone marrow biopsies from myeloma patients revealed a strong positive correlation between the levels of HGF and heparanase, an endoglucuronidase known to promote aggressive tumor behavior. In vitro, addition of recombinant heparanase to myeloma cells or transfection of myeloma cell lines with the cDNA for heparanase significantly increased tumor cell expression and secretion of biologically active HGF. Shed syndecan-1, whose levels in myeloma are also enhanced by heparanase expression, binds to secreted HGF. This syndecan-1-HGF complex is active as shown by its ability to stimulate paracrine signaling via c-Met, the cell surface receptor for HGF. Surprisingly, heparanase enzyme activity was not required for up-regulation of HGF expression by the tumor cells. This is in contrast to the heparanase-mediated enhanced syndecan-1 shedding, which does require activity of the enzyme. This suggests that two different functional domains within the heparanase enzyme (the enzyme active site and a separate site) contribute to events leading to enhanced HGF signaling. These findings demonstrate a novel mechanism driving the HGF pathway whereby heparanase stimulates an increase in both HGF expression and syndecan-1 shedding to enhance HGF signaling. This work also provides further mechanistic insight into the dynamic role of heparanase in driving aggressive tumor progression. Hepatocyte growth factor (HGF) is a heparin-binding cytokine that enhances growth, motility, and angiogenesis of many tumor types, including multiple myeloma where it is often highly expressed. However, little is known regarding what controls HGF level and activity in these tumors. Evaluation of bone marrow biopsies from myeloma patients revealed a strong positive correlation between the levels of HGF and heparanase, an endoglucuronidase known to promote aggressive tumor behavior. In vitro, addition of recombinant heparanase to myeloma cells or transfection of myeloma cell lines with the cDNA for heparanase significantly increased tumor cell expression and secretion of biologically active HGF. Shed syndecan-1, whose levels in myeloma are also enhanced by heparanase expression, binds to secreted HGF. This syndecan-1-HGF complex is active as shown by its ability to stimulate paracrine signaling via c-Met, the cell surface receptor for HGF. Surprisingly, heparanase enzyme activity was not required for up-regulation of HGF expression by the tumor cells. This is in contrast to the heparanase-mediated enhanced syndecan-1 shedding, which does require activity of the enzyme. This suggests that two different functional domains within the heparanase enzyme (the enzyme active site and a separate site) contribute to events leading to enhanced HGF signaling. These findings demonstrate a novel mechanism driving the HGF pathway whereby heparanase stimulates an increase in both HGF expression and syndecan-1 shedding to enhance HGF signaling. This work also provides further mechanistic insight into the dynamic role of heparanase in driving aggressive tumor progression. IntroductionHeparanase, an endo-β-d-glucuronidase capable of cleaving intact heparan sulfate chains from proteoglycans, is up-regulated in a wide variety of human cancers and has been associated with promoting an array of cellular events leading to enhanced tumor progression (1Vlodavsky I. Goldshmidt O. Zcharia E. Atzmon R. Rangini-Guatta Z. Elkin M. Peretz T. Friedmann Y. Semin. Cancer Biol. 2002; 12: 121-129Crossref PubMed Scopus (208) Google Scholar). In addition to its enzymatic glycosidase activity, various nonenzymatic roles of heparanase such as enhancement of AKT signaling have also been described (2Fux L. Ilan N. Sanderson R.D. Vlodavsky I. Trends Biochem. Sci. 2009; 34: 511-519Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar). In multiple myeloma, data from in vitro and in vivo models coupled with analysis of clinical samples have identified heparanase as a promoter of tumor angiogenesis, growth, and metastasis (3Kelly T. Miao H.Q. Yang Y. Navarro E. Kussie P. Huang Y. MacLeod V. Casciano J. Joseph L. Zhan F. Zangari M. Barlogie B. Shaughnessy J. Sanderson R.D. Cancer Res. 2003; 63: 8749-8756PubMed Google Scholar, 4Yang Y. Macleod V. Miao H.Q. Theus A. Zhan F. Shaughnessy Jr., J.D. Sawyer J. Li J.P. Zcharia E. Vlodavsky I. Sanderson R.D. J. Biol. Chem. 2007; 282: 13326-13333Abstract Full Text Full Text PDF PubMed Scopus (219) Google Scholar, 5Yang Y. Macleod V. Bendre M. Huang Y. Theus A.M. Miao H.Q. Kussie P. Yaccoby S. Epstein J. Suva L.J. Kelly T. Sanderson R.D. Blood. 2005; 105: 1303-1309Crossref PubMed Scopus (117) Google Scholar, 6Purushothaman A. Uyama T. Kobayashi F. Yamada S. Sugahara K. Rapraeger A.C. Sanderson R.D. Blood. 2010; 115: 2449-2457Crossref PubMed Scopus (188) Google Scholar, 7Purushothaman A. Chen L. Yang Y. Sanderson R.D. J. Biol. Chem. 2008; 283: 32628-32636Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). Together these findings indicate that heparanase is a key regulator of myeloma progression.Many of the pro-tumorigenic effects of heparanase in myeloma have been traced to heparanase-stimulated up-regulation of syndecan-1 expression and shedding (2Fux L. Ilan N. Sanderson R.D. Vlodavsky I. Trends Biochem. Sci. 2009; 34: 511-519Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar, 4Yang Y. Macleod V. Miao H.Q. Theus A. Zhan F. Shaughnessy Jr., J.D. Sawyer J. Li J.P. Zcharia E. Vlodavsky I. Sanderson R.D. J. Biol. Chem. 2007; 282: 13326-13333Abstract Full Text Full Text PDF PubMed Scopus (219) Google Scholar). Syndecan-1, a heparan sulfate proteoglycan, is expressed on most myeloma tumor cells and is a critical determinant of myeloma cell survival and growth (8Khotskaya Y.B. Dai Y. Ritchie J.P. MacLeod V. Yang Y. Zinn K. Sanderson R.D. J. Biol. Chem. 2009; 284: 26085-26095Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar). Heparanase stimulates the synthesis and shedding of syndecan-1 via increased expression of two sheddases, MMP-9 and uPA 3The abbreviations used are uPA, urokinase-type plasminogen activator; HGF, hepatocyte growth factor; RANKL, receptor activator for nuclear factor κB ligand; IP, immunoprecipitation; HPSE, heparanase. (7Purushothaman A. Chen L. Yang Y. Sanderson R.D. J. Biol. Chem. 2008; 283: 32628-32636Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). Syndecan-1 remains biologically active after it is shed from cells and can control the localization and availability of many heparin-binding growth factors (9Sanderson R.D. Yang Y. Clin. Exp. Metastasis. 2008; 25: 149-159Crossref PubMed Scopus (99) Google Scholar). Using in vivo models of myeloma, our laboratory has demonstrated the synergistic action of heparanase and shed syndecan-1. For example, shed syndecan-1 binds to vascular endothelial growth factor, anchoring it close to the matrix and thereby promoting endothelial cell invasion (6Purushothaman A. Uyama T. Kobayashi F. Yamada S. Sugahara K. Rapraeger A.C. Sanderson R.D. Blood. 2010; 115: 2449-2457Crossref PubMed Scopus (188) Google Scholar).Hepatocyte growth factor (HGF), a heparin-binding cytokine, is primarily expressed by mesenchymal cells and influences epithelial and endothelial cell behavior in a paracrine manner (10Neuss S. Becher E. Wöltje M. Tietze L. Jahnen-Dechent W. Stem Cells. 2004; 22: 405-414Crossref PubMed Scopus (302) Google Scholar, 11Birchmeier C. Birchmeier W. Gherardi E. Vande Woude G.F. Nat. Rev. Mol. Cell Biol. 2003; 4: 915-925Crossref PubMed Scopus (2209) Google Scholar). The pleiotropic effects of HGF are mediated via its binding to the proto-oncogenic c-met receptor (12Ma P.C. Maulik G. Christensen J. Salgia R. Cancer Metastasis Rev. 2003; 22: 309-325Crossref PubMed Scopus (443) Google Scholar). Uniquely in multiple myeloma, HGF is synthesized by tumor cells (13Börset M. Hjorth-Hansen H. Seidel C. Sundan A. Waage A. Blood. 1996; 88: 3998-4004Crossref PubMed Google Scholar), and its gene expression is higher than other known growth factors, making it one of the most highly expressed soluble chemokines in myeloma patients (14Zhan F. Hardin J. Kordsmeier B. Bumm K. Zheng M. Tian E. Sanderson R. Yang Y. Wilson C. Zangari M. Anaissie E. Morris C. Muwalla F. van Rhee F. Fassas A. Crowley J. Tricot G. Barlogie B. Shaughnessy Jr., J. Blood. 2002; 99: 1745-1757Crossref PubMed Scopus (562) Google Scholar). Elevated levels of HGF in the serum of myeloma patients are associated with poor prognosis (15Seidel C. Børset M. Turesson I. Abildgaard N. Sundan A. Waage A. Blood. 1998; 91: 806-812Crossref PubMed Google Scholar) and have been shown to regulate tumor angiogenesis (16You W.K. McDonald D.M. BMB Rep. 2008; 41: 833-839Crossref PubMed Google Scholar), cell migration, survival (17Lesko E. Majka M. Front. Biosci. 2008; 13: 1271-1280Crossref PubMed Scopus (96) Google Scholar), and bone disease in myeloma (18Hjertner O. Torgersen M.L. Seidel C. Hjorth-Hansen H. Waage A. Børset M. Sundan A. Blood. 1999; 94: 3883-3888Crossref PubMed Google Scholar). Surprisingly, very little is understood about the molecular mechanisms that control HGF expression in myeloma. Studies reveal that levels of soluble syndecan-1 correlate positively with levels of HGF expression and regulate its signaling in myeloma (19Derksen P.W. Keehnen R.M. Evers L.M. van Oers M.H. Spaargaren M. Pals S.T. Blood. 2002; 99: 1405-1410Crossref PubMed Scopus (227) Google Scholar, 20Seidel C. Børset M. Hjertner O. Cao D. Abildgaard N. Hjorth-Hansen H. Sanderson R.D. Waage A. Sundan A. Blood. 2000; 96: 3139-3146Crossref PubMed Google Scholar). This observation, along with the established association between heparanase and increased shedding of syndecan-1, points to a novel role for heparanase in regulating HGF activity.In this study, using both in vitro and in vivo models of myeloma, we find that heparanase significantly enhances HGF expression along with the elevation of syndecan-1 shedding. The secreted HGF binds to the shed syndecan-1 and enhances its bioactivity. Interestingly, although heparanase enzyme activity is required for enhanced syndecan-1 shedding, the active enzyme is not required for enhanced HGF synthesis. This indicates that heparanase activates HGF signaling via a novel dual mechanism that likely involves different functional domains of the enzyme. These findings provide unique insight into how HGF expression and activity are up-regulated in myeloma and further establish heparanase as a critical modulator of myeloma disease progression.DISCUSSIONIn this study, we demonstrate a novel and dynamic role for heparanase in enhancing HGF signaling by stimulating myeloma tumor cells to secrete high levels of HGF and by enhancing shedding of syndecan-1. Within the tumor microenvironment, soluble HGF and shed syndecan-1 bind together to form a complex that activates c-met signaling much better than HGF alone. Importantly, we show that the increase in HGF expression is independent of heparanase enzyme activity, although in contrast, as shown previously, the enhanced shedding of syndecan-1 is dependent on heparanase enzyme activity. Thus, heparanase is likely driving enhanced HGF signaling via two distinct mechanisms that merge when the HGF binds to syndecan-1. Given the established role of HGF signaling in driving growth and behavior of both myeloma cells and host cells within tumors, these findings underscore the importance of heparanase in myeloma progression and further validate it as a therapeutic target.High expression of HGF and its effects in myeloma are well established (34Børset M. Seidel C. Hjorth-Hansen H. Waage A. Sundan A. Leuk. Lymphoma. 1999; 32: 249-256Crossref PubMed Scopus (47) Google Scholar). However, the underlying mechanisms triggering enhanced HGF levels and activity are largely unexplored. Our finding that heparanase enhances HGF expression is consistent with our previous work showing that heparanase up-regulates transcription of a number of genes that drive the aggressive tumor phenotype. For example, heparanase enhances myeloma cell expression of VEGF and proteases (MMP-9 and uPA). Enhanced expression of these molecules results from heparanase-stimulated signaling via ERK (6Purushothaman A. Uyama T. Kobayashi F. Yamada S. Sugahara K. Rapraeger A.C. Sanderson R.D. Blood. 2010; 115: 2449-2457Crossref PubMed Scopus (188) Google Scholar, 7Purushothaman A. Chen L. Yang Y. Sanderson R.D. J. Biol. Chem. 2008; 283: 32628-32636Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). However, this is not likely the mechanism driving enhanced HGF expression because high levels of active ERK in HPSE-high cells are dependent upon the enzymatic activity of heparanase (7Purushothaman A. Chen L. Yang Y. Sanderson R.D. J. Biol. Chem. 2008; 283: 32628-32636Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). In contrast, in the present study up-regulation of HGF was stimulated by enzymatically inactive forms of heparanase. This finding strongly suggests that stimulation of HGF expression is not dependent on the enzyme active site of the heparanase molecule but resides in a different domain. Predictions of heparanase structure point to a TIM-barrel domain that bears the enzyme active site and to a C-terminal domain (C-domain) responsible for nonenzymatic functions of heparanase (2Fux L. Ilan N. Sanderson R.D. Vlodavsky I. Trends Biochem. Sci. 2009; 34: 511-519Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar). Functionally, the C-domain of heparanase can mediate enhanced Akt phosphorylation (35Fux L. Feibish N. Cohen-Kaplan V. Gingis-Velitski S. Feld S. Geffen C. Vlodavsky I. Ilan N. Cancer Res. 2009; 69: 1758-1767Crossref PubMed Scopus (86) Google Scholar). Interestingly, it was recently demonstrated that induction of Akt phosphorylation leads to enhanced HGF expression and secretion in human mesenchymal stem cells (36Zhang A. Wang Y. Ye Z. Xie H. Zhou L. Zheng S. J. Cell. Biochem. 2010; 111: 469-475Crossref PubMed Scopus (46) Google Scholar). However, heparanase did not alter levels of Akt phosphorylation in the myeloma cells studied here 4V. C. Ramani, unpublished observations. indicating that the C-domain likely has functions that have not yet been uncovered.Our findings demonstrate that myeloma cells produce levels of HGF and syndecan-1 that are appropriate for forming an effective complex that stimulates signaling. This is important because previous studies have shown that when levels of syndecan-1 are too high relative to levels of HGF, signaling activity is actually inhibited. Conversely, when concentrations of syndecan-1 are too low, they have no effect on HGF signaling (20Seidel C. Børset M. Hjertner O. Cao D. Abildgaard N. Hjorth-Hansen H. Sanderson R.D. Waage A. Sundan A. Blood. 2000; 96: 3139-3146Crossref PubMed Google Scholar). The level of heparanase-induced syndecan-1 is therefore crucial in determining HGF activity and c-met signaling in vivo thus providing a sensitive mechanism to modulate tumor behavior.The positive impact of heparanase expression on HGF activity in myeloma could have multiple effects on progression of this cancer. It has been shown that recombinant HGF enhances myeloma tumor cell proliferation and inhibits apoptosis in vitro (37Derksen P.W. de Gorter D.J. van M. A.C. Spaargaren M. Pals S.T. 2003; PubMed Scopus Google Scholar). However, it is important to that the effects of HGF on myeloma proliferation are upon with high levels of recombinant HGF (37Derksen P.W. de Gorter D.J. van M. A.C. Spaargaren M. Pals S.T. 2003; PubMed Scopus Google Scholar). In contrast, cells within the myeloma tumor microenvironment, (18Hjertner O. Torgersen M.L. Seidel C. Hjorth-Hansen H. Waage A. Børset M. Sundan A. Blood. 1999; 94: 3883-3888Crossref PubMed Google Scholar), strongly to levels of HGF in increased it is likely that a role for heparanase-stimulated HGF in vivo is largely mediated via paracrine c-met signaling. In addition to stimulation of paracrine signaling pathway active in is present in endothelial cells where HGF signaling enhances angiogenesis F. M. E. M. L. G. L. A. J. Cell Biol. PubMed Scopus Google Scholar). that signaling is an important of angiogenesis has to to this pathway K. T. Cancer Sci. 2003; 94: PubMed Scopus Google Scholar, K. K. K. H. M. T. Cancer Res. 2000; Google Scholar, K. K. K. H. M. T. 1998; PubMed Scopus Google also that in the studied HGF and syndecan-1 together stimulated much higher than HGF and that this to an increase in expression in cells. a key regulator of is a of c-met signaling (18Hjertner O. Torgersen M.L. Seidel C. Hjorth-Hansen H. Waage A. Børset M. Sundan A. Blood. 1999; 94: 3883-3888Crossref PubMed Google Scholar). inhibits bone in vitro PubMed Scopus Google Scholar) and bone P. M. 2002; PubMed Scopus Google Scholar) via multiple independent including up-regulation of C. E. 2007; PubMed Scopus Google Scholar, R. M. Shaughnessy J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, E. N. Zhou H. T. M. T. D.J. T. J. Exp. 1996; PubMed Scopus Google Scholar, O. A. A. I. Y. 2003; 32: PubMed Scopus Google Scholar, A. S. 1998; PubMed Google Scholar). these data indicate that heparanase contribute to myeloma bone disease by the In addition to these effects on heparanase also stimulates expression of by myeloma tumor cells Y. Y. L. Suva L.J. Sanderson R.D. Cancer Res. 2010; PubMed Scopus Google Scholar). effect of heparanase-mediated signaling could in driving mechanisms that a that leads to and of many myeloma patients Sanderson R.D. Wilson PubMed Scopus Google Scholar). have demonstrated that high levels of syndecan-1 are present in bone marrow of myeloma patients Sanderson R.D. Wilson PubMed Scopus Google Scholar). This syndecan-1 could of of HGF making it for tumor cells that thereby to bone disease and stimulating angiogenesis, of which contribute to of studies have the importance of shed syndecan-1 in regulating the of including different of cancers T. Y. J. 2010; PubMed Scopus Google Scholar). The ability of heparanase to enhance syndecan-1 shedding and the effect of shed syndecan-1 in regulating the activity of various growth factors crucial in the of where are high levels of shed syndecan-1 present Cohen-Kaplan V. I. Sanderson R.D. Ilan N. Vlodavsky I. J. 2010; PubMed Scopus Google the findings here provide novel into how heparanase HGF activity in myeloma. the expression and activity of HGF, heparanase very likely tumor angiogenesis, bone and the to in myeloma. heparanase can strongly drive the of molecules that promote heparanase a unique of for bone of heparanase as therapeutic for the in Together these results further establish heparanase as a regulator of myeloma and to other cancers where HGF a role in tumor progression. IntroductionHeparanase, an endo-β-d-glucuronidase capable of cleaving intact heparan sulfate chains from proteoglycans, is up-regulated in a wide variety of human cancers and has been associated with promoting an array of cellular events leading to enhanced tumor progression (1Vlodavsky I. Goldshmidt O. Zcharia E. Atzmon R. Rangini-Guatta Z. Elkin M. Peretz T. Friedmann Y. Semin. Cancer Biol. 2002; 12: 121-129Crossref PubMed Scopus (208) Google Scholar). In addition to its enzymatic glycosidase activity, various nonenzymatic roles of heparanase such as enhancement of AKT signaling have also been described (2Fux L. Ilan N. Sanderson R.D. Vlodavsky I. Trends Biochem. Sci. 2009; 34: 511-519Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar). In multiple myeloma, data from in vitro and in vivo models coupled with analysis of clinical samples have identified heparanase as a promoter of tumor angiogenesis, growth, and metastasis (3Kelly T. Miao H.Q. Yang Y. Navarro E. Kussie P. Huang Y. MacLeod V. Casciano J. Joseph L. Zhan F. Zangari M. Barlogie B. Shaughnessy J. Sanderson R.D. Cancer Res. 2003; 63: 8749-8756PubMed Google Scholar, 4Yang Y. Macleod V. Miao H.Q. Theus A. Zhan F. Shaughnessy Jr., J.D. Sawyer J. Li J.P. Zcharia E. Vlodavsky I. Sanderson R.D. J. Biol. Chem. 2007; 282: 13326-13333Abstract Full Text Full Text PDF PubMed Scopus (219) Google Scholar, 5Yang Y. Macleod V. Bendre M. Huang Y. Theus A.M. Miao H.Q. Kussie P. Yaccoby S. Epstein J. Suva L.J. Kelly T. Sanderson R.D. Blood. 2005; 105: 1303-1309Crossref PubMed Scopus (117) Google Scholar, 6Purushothaman A. Uyama T. Kobayashi F. Yamada S. Sugahara K. Rapraeger A.C. Sanderson R.D. Blood. 2010; 115: 2449-2457Crossref PubMed Scopus (188) Google Scholar, 7Purushothaman A. Chen L. Yang Y. Sanderson R.D. J. Biol. Chem. 2008; 283: 32628-32636Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). Together these findings indicate that heparanase is a key regulator of myeloma progression.Many of the pro-tumorigenic effects of heparanase in myeloma have been traced to heparanase-stimulated up-regulation of syndecan-1 expression and shedding (2Fux L. Ilan N. Sanderson R.D. Vlodavsky I. Trends Biochem. Sci. 2009; 34: 511-519Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar, 4Yang Y. Macleod V. Miao H.Q. Theus A. Zhan F. Shaughnessy Jr., J.D. Sawyer J. Li J.P. Zcharia E. Vlodavsky I. Sanderson R.D. J. Biol. Chem. 2007; 282: 13326-13333Abstract Full Text Full Text PDF PubMed Scopus (219) Google Scholar). Syndecan-1, a heparan sulfate proteoglycan, is expressed on most myeloma tumor cells and is a critical determinant of myeloma cell survival and growth (8Khotskaya Y.B. Dai Y. Ritchie J.P. MacLeod V. Yang Y. Zinn K. Sanderson R.D. J. Biol. Chem. 2009; 284: 26085-26095Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar). Heparanase stimulates the synthesis and shedding of syndecan-1 via increased expression of two sheddases, MMP-9 and uPA 3The abbreviations used are uPA, urokinase-type plasminogen activator; HGF, hepatocyte growth factor; RANKL, receptor activator for nuclear factor κB ligand; IP, immunoprecipitation; HPSE, heparanase. (7Purushothaman A. Chen L. Yang Y. Sanderson R.D. J. Biol. Chem. 2008; 283: 32628-32636Abstract Full Text Full Text PDF PubMed Scopus (168) Google Scholar). Syndecan-1 remains biologically active after it is shed from cells and can control the localization and availability of many heparin-binding growth factors (9Sanderson R.D. Yang Y. Clin. Exp. Metastasis. 2008; 25: 149-159Crossref PubMed Scopus (99) Google Scholar). Using in vivo models of myeloma, our laboratory has demonstrated the synergistic action of heparanase and shed syndecan-1. For example, shed syndecan-1 binds to vascular endothelial growth factor, anchoring it close to the matrix and thereby promoting endothelial cell invasion (6Purushothaman A. Uyama T. Kobayashi F. Yamada S. Sugahara K. Rapraeger A.C. Sanderson R.D. Blood. 2010; 115: 2449-2457Crossref PubMed Scopus (188) Google Scholar).Hepatocyte growth factor (HGF), a heparin-binding cytokine, is primarily expressed by mesenchymal cells and influences epithelial and endothelial cell behavior in a paracrine manner (10Neuss S. Becher E. Wöltje M. Tietze L. Jahnen-Dechent W. Stem Cells. 2004; 22: 405-414Crossref PubMed Scopus (302) Google Scholar, 11Birchmeier C. Birchmeier W. Gherardi E. Vande Woude G.F. Nat. Rev. Mol. Cell Biol. 2003; 4: 915-925Crossref PubMed Scopus (2209) Google Scholar). The pleiotropic effects of HGF are mediated via its binding to the proto-oncogenic c-met receptor (12Ma P.C. Maulik G. Christensen J. Salgia R. Cancer Metastasis Rev. 2003; 22: 309-325Crossref PubMed Scopus (443) Google Scholar). Uniquely in multiple myeloma, HGF is synthesized by tumor cells (13Börset M. Hjorth-Hansen H. Seidel C. Sundan A. Waage A. Blood. 1996; 88: 3998-4004Crossref PubMed Google Scholar), and its gene expression is higher than other known growth factors, making it one of the most highly expressed soluble chemokines in myeloma patients (14Zhan F. Hardin J. Kordsmeier B. Bumm K. Zheng M. Tian E. Sanderson R. Yang Y. Wilson C. Zangari M. Anaissie E. Morris C. Muwalla F. van Rhee F. Fassas A. Crowley J. Tricot G. Barlogie B. Shaughnessy Jr., J. Blood. 2002; 99: 1745-1757Crossref PubMed Scopus (562) Google Scholar). Elevated levels of HGF in the serum of myeloma patients are associated with poor prognosis (15Seidel C. Børset M. Turesson I. Abildgaard N. Sundan A. Waage A. Blood. 1998; 91: 806-812Crossref PubMed Google Scholar) and have been shown to regulate tumor angiogenesis (16You W.K. McDonald D.M. BMB Rep. 2008; 41: 833-839Crossref PubMed Google Scholar), cell migration, survival (17Lesko E. Majka M. Front. Biosci. 2008; 13: 1271-1280Crossref PubMed Scopus (96) Google Scholar), and bone disease in myeloma (18Hjertner O. Torgersen M.L. Seidel C. Hjorth-Hansen H. Waage A. Børset M. Sundan A. Blood. 1999; 94: 3883-3888Crossref PubMed Google Scholar). Surprisingly, very little is understood about the molecular mechanisms that control HGF expression in myeloma. Studies reveal that levels of soluble syndecan-1 correlate positively with levels of HGF expression and regulate its signaling in myeloma (19Derksen P.W. Keehnen R.M. Evers L.M. van Oers M.H. Spaargaren M. Pals S.T. Blood. 2002; 99: 1405-1410Crossref PubMed Scopus (227) Google Scholar, 20Seidel C. Børset M. Hjertner O. Cao D. Abildgaard N. Hjorth-Hansen H. Sanderson R.D. Waage A. Sundan A. Blood. 2000; 96: 3139-3146Crossref PubMed Google Scholar). This observation, along with the established association between heparanase and increased shedding of syndecan-1, points to a novel role for heparanase in regulating HGF activity.In this study, using both in vitro and in vivo models of myeloma, we find that heparanase significantly enhances HGF expression along with the elevation of syndecan-1 shedding. The secreted HGF binds to the shed syndecan-1 and enhances its bioactivity. Interestingly, although heparanase enzyme activity is required for enhanced syndecan-1 shedding, the active enzyme is not required for enhanced HGF synthesis. This indicates that heparanase activates HGF signaling via a novel dual mechanism that likely involves different functional domains of the enzyme. These findings provide unique insight into how HGF expression and activity are up-regulated in myeloma and further establish heparanase as a critical modulator of myeloma disease progression.